In a step toward an ultra-secure global communication network, scientists have transmitted a quantum-encrypted message through the air in real-world city conditions.

The breakthrough marks the first time researchers have demonstrated that more than one bit of information per photon could be sent across this type of environment, in a phenomenon known as 4D encryption.

The team demonstrated 4D quantum encryption between two buildings situated nearly one-fifth of a mile apart (.3 km) – and eventually, they say it could be used to link Earth with moving objects such as an airplane, or even satellites in space.

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The breakthrough marks the first time researchers have demonstrated that more than one bit of information per photon could be sent across this type of environment, in a phenomenon known as 4D encryption. An artist's impression is pictured

THE EXPERIMENT

In the study, the researchers demonstrated 4D quantum encryption over a free-space optical network for the first time, allowing for four possibilities instead of just two.

Their technique allows for more information, with the possibilities of 01, 10, 00, or 11.

The team used laboratory optical setups, covered with wooden boxes for protection, atop two rooftops .3 kilometers apart.

The experiments revealed they could transmit 1.6 times more information per photon using 4D encryption, even when turbulence was present.

In addition to sending more information, the researchers say it also makes the system more secure, as it can withstand more signal-obscuring noise.

This type of interference can come from turbulent air, failed electronics, malfunctioning detectors, or attempts to intercept the data, according to the team.

The experiments led by researchers at the University of Ottawa involved pairs of photons, in which each individual photon was encoded with two bits of information.

This is considered to be a high-dimensional form of encryption, creating a more advanced system than 2D encryption, where each photon encodes just one bit.

As eight bits are required to encode a single letter, adding more information per photon would make for much faster transmission.

In the study, the researchers demonstrated 4D quantum encryption over a free-space optical network for the first time, allowing for four possibilities instead of just two.

The team used laboratory optical setups, covered with wooden boxes for protection, atop two rooftops .3 kilometers apart.

The experiments revealed they could transmit 1.6 times more information per photon using 4D encryption, even when turbulence was present.

And, they had an error rate of just 11 percent, which falls below the 19 percent threshold needed for a secure connection.

‘Our work is the first to send messages in a secure manner using high-dimensional quantum encryption in realistic city conditions, including turbulence,’ said research team lead, Ebrahim Karimi.

‘The secure, free-space communication scheme we demonstrated could potentially link Earth with satellites, securely connect places where it is too expensive to install fiber, or be used for encrypted communication with a moving object, such as an airplane.’

Their technique allows for more information, with the possibilities of 01, 10, 00, or 11.

In addition, the researchers say it also makes the system more secure, as it can withstand more signal-obscuring noise.

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The researchers say a 4D system is more secure, as it can withstand more signal-obscuring noise. This type of interference can come from turbulent air, failed electronics, malfunctioning detectors, or attempts to intercept the data, according to the team. A stock image is shown

This type of interference can come from turbulent air, failed electronics, malfunctioning detectors, or attempts to intercept the data, according to the team.

‘This higher noise threshold means that when 2D quantum encryption fails, you can try to implement 4D because it, in principle, is more secure and more noise resistant,’ Karimi said.

To achieve free-space quantum encryption on a global scale, secure networks that link ground stations and satellites will be a necessity.

Now that they’ve determined that it is possible to achieve 4D quantum encryption outside, researchers can move on to further tests to simulate the transmission of these signals to satellites.

CHINA'S 'UNHACKABLE' NETWORK

China has built one of the world's largest hack-proof computer networks in a bid to protect state secrets from prying eyes.

An advanced communications system will secure government, financial, military and other information from eavesdroppers.

Current technology relies on mathematical equations, that are too complex for most computers to crack.

But, as processing power continues to grow, these equations have to be made increasingly complex to keep up.

And there are fears that the next generation of quantum computers will make this method of protection obsolete.

Special keys are embedded into particles of light, which are needed to decode the information.

The system has one cable for sharing photons and another for data transfer.

A ‘three-kilometer test,’ for example, in which signals are sent horizontally through the air across three kilometers, is about equal to sending a signal through Earth’s atmosphere to a satellite.

‘After bringing equipment that would normally be used in a clean, isolated lab environment to a rooftop that is exposed to the elements and has no vibration isolation, it was very rewarding to see results showing that we could transmit secure data,’ said Alicia Sit, an undergraduate student in Karimi’s lab.

Next, the team plans to create a network involving three links, each about 5.6 kilometers apart.

This will rely on a technology known as adaptive optics to combat turbulence.

And eventually, they hope to link their system to the city’s existing network.

According to Sit, ‘Our long-term goal is to implement a quantum communication network with multiple links but using more than four dimensions while trying to get around the turbulence.’